This invention relates to power semiconductor device packages, and more specifically, to a method of insulating power semiconductor chips from one another in a package by physically separating them within a single multichip package, and the resultant multichip package.
Oftentimes more than one silicon wafer, or xe2x80x9cchipxe2x80x9d is present in an integrated circuit package. For instance, one integrated circuit package may contain a signal processing chip, a function control chip, and an amplifying chip all within the same integrated circuit package. This is especially true as the miniaturization of electronic devices continues, requiring one-package solutions where previously multi-package solutions were acceptable.
Shown in FIG. 1a is a representation of a twenty pin Dual In-Line Package (DIP). Shown is an integrated circuit (IC) package 10, having twenty pins labeled 12, ten pins on each side of the IC package 10. FIG. 1b shows the IC package 10 without a top cover, giving a view of how the pins 12 are connected within the IC package. The IC package 10 contains a chip 20 that has several bonding pads 14. Each bonding pad 14 is connected to one of the pins 12 of the IC package 10 in a conventional manner, such as by thermosonic or ultrasonic bonding. The chip 20 is coupled to eight of the twenty pins 12 of the IC package 10. The other twelve pins 12 of the IC package 10 are coupled to the bonding pads 14 of a chip 30.
The chips 20 and 30 are attached to a common slug 40, shown in FIG. 2. Often the common slug 40 is made from a metal material such as copper, but any suitable material can be used. When the common slug 40 is made from copper, the chips 20 and 30 can be directly soldered to, or otherwise physically attached to the slug, such as by eutectic bonding. The common slug 40 provides a stable base for handling during the creation of the IC package 10. Additionally, the slug acts as a large heat dissipater, removing heat from the chips 20 and 30 developed during their operation.
However, sometimes the regular operation of the individual chips 20 and 30 causes them to interfere with one another during operation. If, for example, the chip 20 produces an electrical signal that interferes with the operation of the chip 30, the common slug 40 carries that electrical signal directly to the chip 30, causing the interference. To prevent such interference, an electrical insulating layer 50 (FIG. 2) is provided between the chip 30 and the common slug 40. This electrical insulating layer can be an adhesive tape, for example, or a layer of molding compound.
The presence of this electrical insulating layer 50 degrades the efficient heat transfer between the chip 30 and the common slug 40. Therefore, the chip 30, when electrically insulated from the common slug 40 by the electrical insulating layer 50, runs at a higher temperature than if it were directly soldered to the common slug 40. This higher temperature can degrade the performance of the chip 30, or even cause it to malfunction. However, in instances where the electrical insulating layer 50 is necessary, the chip cannot be soldered directly to the common slug 40 otherwise the electrical interference between the chip 20 and chip 30 would be present.
One embodiment of the invention presents a multichip integrated circuit package having at least two chips electrically isolated from one another. Within the multichip integrated circuit package is a slug that is directly coupled to at least two chips, without any intervening insulating layers. The slug is physically separated at an appropriate place between the two chips, so that electrical interference between the two chips is eliminated.
Another embodiment of the invention presents a method for creating a multichip integrated circuit package having at least two chips electrically isolated from one another. The method begins with directly attaching the two chips to a heat dissipating slug, preferably by soldering the chips to the slug. In one embodiment, the heat dissipating slug has a pre-cut groove running between the chips. Once the chips are attached to the slug, the slug is molded into the multichip integrated circuit package. Then, the slug is physically separated into two pieces from the underside, the separation running along the pre-cut groove. In one embodiment, the slug is cut with a saw.